tonight law enforcement sources tell abc news that the young man seen on this surveillance tape, calmly walking through the crowd with a bomb in his bag, is now being cooperative with investigators. he has trouble speaking because of gunshot wounds to his neck, but he's communicating through writing, nodding his head, and making short vocalizations. based on what he's told them, investigators are convinced there are no more ongoing plots. and tonight abc news has learned dzhokhar tsarnaev told investigators, they learned to build a bomb on the internet. today dzhokhar tsarnaev was officially charged with using, and conspiring to use, a weapon of mass destruction. the complaint also contains vivid, new details about the chaotic events of last thursday night when the brothers tsarnaev allegedly carjacked a man. the victim describes one of the brothers getting in the car and saying, "did you hear about the boston explosion? i did that." the victim says the brother then removed a magazine from his gun, displayed a bullet and said, i am serious. the victim later escaped when the brothers got